1. Field of the Invention
The present invention relates to a method of marking an article having at least a polyolefin, preferably polyethylene or polypropylene, surface by exposing said surface to the action of a laser beam.
2. Description of the Prior Art
It is known in the art to provide plastic materials in the form of containers, covers of containers and similar articles with a mark, by subjecting the plastic material to the action of a laser beam. Polyvinylchloride and polystyrene absorb the energy of such a laser beam so that the surface of the plastic materials is heated to a temperature involving decomposition of the plastic thus providing a black colored mark consisting of decomposed plastics.
Additives added to these plastics in order to obtain the desired properties and color do not hamper the laser beam action.
Plastic materials consisting of polyolefins, such as polypropylene and polyethylene, have the drawback, however, that they cannot be marked in the same way by means of a laser beam. This is particularly disadvantageous as on the one hand polypropylene and polyethylene due to their easy working and the attractive appearance which they give to packings are used on a large scale for packing foods, while on the other hand manufacturers of food who have to apply a well legible mark on packages etc., for instance, the date of final consumption, the production date or other similar marks cannot apply these marks on the respective materials, by means of a laser beam.
Up till now marking of polyolefin surfaces is obtained by subjecting polyolefin surfaces containing a dye, to the action of a laser beam which destroys the dye, so that the mark consists of discoloured parts of the container.